In a sophisticated seat-belt retractor that has a reversible drive with an electric motor for the winding and unwinding function as well as for the belt tensioning in case of a possible emergency, the belt spool is blocked by a mechanical locking system after the belt webbing has been tensioned. The locking system generally comprises a coupling pawl pivotally mounted in the retractor frame and a cooperating locking toothing on the periphery of the belt spool. The toothing geometry is designed so that, after an initial contact between the coupling pawl and the teeth of the locking toothing, the coupling pawl is positively pulled into full engagement in a gap of the locking toothing. In other words, the locking toothing geometry is provided with an undercut. Since the tensioning of the belt webbing is but a measure of precaution, normal operation of the seat-belt retractor must be restored after a locking has occurred. With such a toothing geometry, however, it is impossible to disengage the coupling pawl from the locking toothing without a prior reverse rotation of the belt spool. Such reverse rotation of the, belt spool can be effected by activating the electric motor in a sense to retract some belt webbing. However, as the belt webbing is already tensioned in such a situation, high demands on the power of the electric motor are made. Moreover, a vehicle occupant would feel an additional belt retraction, with a consequential additional tension, to be unpleasant.